Transmitting data with video

ABSTRACT

Signal processors for permitting the transparent, simultaneous transmission and reception of a secondary data signal with a video signal in the video band is disclosed. The signal processor in the transmitter rasterizes the data at the horizontal scanning rate and modulates the data with a data carrier at a non-integral multiple of the horizontal scanning rate to obtain frequency interleaving. The data is transmitted during the active video portion of each video line.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to transmitting two signals on one communicationchannel and more particularly transmitting data during the active videoportion of a video signal.

2. Description of the Prior Art

Several techniques have been developed to allow the transmission of twosignals on the same communications channel. When the communicationschannel is a specified bandwidth of the spectra, these methods includetime division multiplexing, transmitting orthogonally polarized waves,transmitting by two transparent methods, each transparent to the otherand frequency interleaving.

In the case of video signals, such as NTSC and PAL signals, severaldifferent methods have been used for transmission of additionalinformation in the band. For example, a chrominance (color) signal istransmitted by frequency interleaving the chrominance signal with theluminance (black and white ) signal. In particular, for the NTSCstandard, the luminance signal and the chrominance signals are frequencyinterleaved. Of course, the chrominance signals are closely related tothe luminance signal and the signals exhibit a high degree ofcorrelation.

There are also intervals where no picture information is beingtransmitted such as during the vertical and horizontal blankingintervals. In some systems, for example close captioned television forthe hearing impaired, the close captioned information is transmittedduring the vertical blanking intervals. Of course, the data rate oftransmission systems using the blanking period is relatively low,typically about 20,000 bits per second. Although such transmission ratesmay be suitable for close caption television, this is far too low forthe suitable transmission of large volumes of information such as the1,544 megabits per second for T1 transmission.

Therefore, it is a first object of this invention to permit transmissionat a higher data rate than those permitted during the blanking period.It is a second object of this invention to permit transmission at thehigher data rate without causing any noticeable interference from thetransmitted information to conventional television receivers. It is yeta third object of this invention to achieve such transmission usingfrequency interleaving.

SUMMARY OF THE INVENTION

These and other objects are achieved through the use of transmission ofsecondary data during the active primary video interval when pixelinformation is being transmitted rather than during the horizontal orvertical sync blanking intervals. The transmitted data is preferablyfrequency interleaved with the chrominance and luminance signal.

The signal processor for use by the transmitter for the novelcommunications system disclosed herein has five portions. A primaryvideo portion, a timing portion, and a video analyzer portion receivethe primary video signal. The timing portion produces a non-integralmultiple of the video horizontal scanning frequency for use by a dataportion for modulation. In addition, the timing portion produces acomposite blanking pulse so that the data portion may rasterize the datato be transmitted.

Another portion, a noise interference reduction portion receives anoutput from the video portion and provides a noise signal representingnoise in the frequency gaps for interleaving of the primary videosignal. That noise signal may be subtracted from the video signal toreduce the noise imposed on the modulated data signal when the video anddata signals are combined.

A secondary data portion receives the secondary data signal, which maybe analog or digital. The secondary data portion rasterizes the datasignal and modulates the data signal so that the modulated data signalis frequency interleaved with the primary video signal.

The data portion rasterizes the data signal to include vertical andhorizontal blanking periods that will coincide with those blankingperiods in the primary video signal when the modulated data signal andthe primary video are combined. The rasterized data signal is thenmodulated by a data carrier so that the modulated data spectral envelopeinterleaves with the primary video envelope. The resultant combinedsignal may be received by ordinary video receivers without noticeableinterference in the video receiver.

The data signal may be recovered by a receiver incorporating aspecialized signal processor. A filter passing those frequenciescontaining the secondary data supplies a data signal to a phasecompensator. The phase compensator eliminates phase shifts induced bythe filter. The output of the compensator may then be demodulated,decoded and derasterized. To accomplish the demodulation, a timingcircuit should be included that generates the data carrier and generatesa system clock including a blanking interval.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram for a signal processor incorporating anembodiment of the instant invention for use in a transmitter.

FIG. 2 is a block diagram for a signal processor incorporating anembodiment of the instant invention for use in a receiver.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an embodiment of the signal processor 10 of the transmitterthat may be used for transmitting secondary digital data at the T1 rateof 1.544 Megabits per second through a transmitter with a primary NTSCcolor video signal. Other embodiments of the invention may be used fortransmitting digital data at other data rates or analog data with eitheran NTSC video signal or another video format signal.

The embodiment 10 comprises five different sections. These sections area primary video section 20, a timing section 30, a video analyzersection 40, a secondary data modulation section 50 and a noise reductionsection 60. An analog summer or adder 70 combines the outputs of thedata modulation section 50, the noise reduction section 60 and theprimary video section 20. It should be noted, however, that the videosection 20, the video analyzer section 40 and the noise reductionsection 60 may not be needed depending upon the data rate of the datasignal, the quality of the primary video signal and channel noise.

A primary video signal, which in this embodiment may be an NTSC colorsignal having a horizontal blanking frequency of 15,734.264 hertz and avertical blanking frequency of 59.940052 hertz is received. The primaryvideo signal comprises luminance and chrominance signals. The NTSCsignal also has vertical and horizontal blanking intervals determined bythe vertical and horizontal sync pulses and an active video intervalbetween blanking intervals. During the active video intervals, the pixelinformation for a line of the video picture is transmitted. However, itshould be understood that the primary video signal may be any rasterizedvideo signal including video formats commonly used in other countriessuch as PAL. The primary video signal, which is at baseband, is suppliedto the primary video section 20, the timing section 30 and the videoanalyzer 40.

The peak to peak amplitude of the primary video signal is limited to apredetermined standard by an automatic gain control amplifier 22 and theblanking level of the video signal is set to a predetermined voltage bya DC restore circuit 24. If the primary video signal is an NTSC signal,the function of the DC restore circuit 24 and the automatic gain controlamplifier 22 is to supply a signal at an output 25 that complies withthe RS 170A standard. If the primary video signal meets the RS 170Astandard, the amplifier 22 and the restore circuit 24 may be eliminated.

The output 25 is supplied to a first analog delay line 26. The length ofthe first analog delay line 26 should at least be equal to the timeperiod required by the video analyzer section 40 to analyze a group ofpixels of the primary video signal as will be described below. Theoutput of the delay line 26 is supplied to a low pass filter 27 thatreduces noise in the upper band of the video signal. The output of thefilter 27 is supplied to a second delay line 28, which provides a delayequal to the delay of the noise interference section 60. The output ofthe primary video section 20 is supplied to a non-inverting input of thesummer 70.

The noise interference section 60 comprises a band pass/comb filter andis preferably the same as the filter 123 in the processor 100 for thereceiver. That filter is called a noise interference reduction device.That filter blocks the frequency bands containing the luminance andchrominance signal information. The output of the noise interferencesection 60 comprises the noise component of the video signal lying inthe frequency bands to be occupied by the modulated data. The noisecomponent is then supplied to an inverting input of the adder 70 toremove that noise component present in the primary video section 20output.

The input data is supplied to a first in first out elastic buffer 52along with an external clock signal. The data clock controls the rate atwhich data is stored in the buffer 52. The rate at which data isoutputted by the elastic buffer 52 is controlled by two signals, asecond, system clock/rasterizing signal 33 provided by the timingsection 30 and an inhibit signal supplied by the video analyzer section40.

The elastic buffer 52 only outputs data at a predetermined rate duringthe active video portions of the signal as indicated by the system clocksignal 33. The system clock 33 is used for rasterizing the data outputof the elastic buffer 52 to create blanking intervals.

No data is outputted from the elastic buffer 52 during blankingintervals. The blanking intervals when no data is outputted from thebuffer are adjusted sufficiently to synchronize the blanking periods ofthe output of the video portion 20 and the data portion 50 to the summer70.

Further, in high speed data transmission such as T1, the elastic buffer52 is inhibited from outputting data during portions of the video linehaving sharp transitions as will be explained in more detail below. Whenthe video analyzer section 40 does not inhibit the elastic buffer, theoutput of the elastic buffer 52 is a rasterized version of the inputsecondary data; i.e., the data has the same duration blanking intervalsand those blanking intervals coincide at the output of the data section50 with the blanking intervals in the video signal at the output of thevideo section 20 when they arrive at the adder 70.

The rasterized, secondary data signal from the buffer 52 is supplied tothe encoder 54, which also receives the system clock 33 and the inhibitsignal from the video analyzer 40. The encoder 54 encodes the data tolimit the bandwidth. The encoder 54 may be a NRZ encoder, an FM encoder,an MFM encoder, a Manchester encoder, a 1,7 RLL encoder, a 2,7 RLLencoder or any other encoder that limits the bandwidth of the rasterizeddata signal output from the elastic buffer 52. In addition, datascramblers and block error correction coders may be included to providesecurity or to improve the bit error rate.

The output of the encoder is supplied to a multiplier 56 for modulatingthe encoded data on a data carrier. The encoded data is phasesynchronized with a data carrier and is amplitude modulated by themultiplier 56. In this particular embodiment, the modulated carrier iseither present or is not present depending upon whether the encoded datais a one or zero. Preferably, no carrier is transmitted during theblanking interval.

However, in other embodiments, different modulation schemes may be used.For low secondary data rate transmissions, the encoded data need not besynchronous with the modulated data and one data bit may be transmittedover several cycles of the data carrier. For higher data rates, wherethe encoded data is synchronous with the data carrier, more than twolevels may be permissible for higher data rate transmission. Forexample, a half cycle may have a zero level peak, a 1/3 maximum levelpeak, a 2/3 maximum level peak and a maximum level peak so that two databits may be transmitted in one half cycle. Other techniques may be usedfor increasing the data rate such as quadrature amplitude modulation,quadrature phase shift keying and phase modulation where the data andthe data carrier are synchronized. Data rates of 280 kilobits per secondhave been found not to require such multibits per half cycle modulationtechniques.

The modulated data carrier including the encoded data is passed througha low pass filter 58 that attenuates the higher sideband. The lowersideband of the data carrier is transmitted by the filter 58.

The output of the low pass filter 58 is supplied to a noninverting inputof the adder 70 for combining the modulated, rasterized secondary datawith the processed video. The timing of the data portion 50 and thevideo portion 20 is such that the blanking intervals in the video signalsupplied to the adder 70 coincide with the inhibited intervals of therasterized modulated data signal. The combined signal from the videoportion 20 and the data portion 50 is a signal at the baseband frequencywith the information for the data signals and the information for thevideo signals frequency interleaved into separate bands respectivelywith minimal overlap. The interleaved signal may then be transmitted atnormal data rates.

The timing section 30 comprises a vertical sync detector, a horizontalsync detector, a color frame detector and phase lock loops that use thedetected signals for generating various timing signals. In particular,the data carrier is generated in this embodiment by dividing thehorizontal scanning rate of the primary video signal by four and thenmultiplying the scanning rate by one thousand and forty three throughthe use of a phase lock loop to generate a data carrier at 4,102,708hertz. Since the data signal has been rasterized and then modulated at anon-integral multiple of the horizontal frequency at the modulator 56,the spectral envelope of the video signal, when combined by the adder 70to the video signal, is frequency interleaved with the video signal.Further, the data carrier should have a known phase relationship withthe color frame.

Although a specific example has been selected for the data carrier,other non-integral multiples may be used. The criteria for the datacarrier are that the data carrier: (1) should be a non-integral multipleof the horizontal scanning frequency, (2) should be preferably greaterthan the chrominance carrier, and (3) should be preferably outside theluminance band but be well enough within the video channel bandwidth sothat there is not likely to be interference with aural channels.

In addition, the timing section uses phase lock loops to generate asystem clock rasterizing signal 33 for outputting data from the elasticbuffer 52. The system clock frequency should be either a submultiple ora multiple of the horizontal scanning frequency. The selection of thesystem clock frequency should be based upon the maximum datatransmission rate during an active video line and the data clock rate.The clock should be inhibited for a period equal to each video andhorizontal blanking interval so that no modulated data is combined withthe video signal at the adder 70 during blanking intervals of theprimary video signal; i.e. the blanking intervals in the output of thevideo 20 and data portion 50 should be synchronized. Further, the systemclock rate should be sufficiently high so that the elastic buffer willnot overflow.

The use of phase lock loops for generating both the system clock and thedata carrier means that the two signals are phase related. This allowsfor transmission by a modulator at higher data rates by, for example,having each half cycle of the data carrier representing one data elementfor transmission.

A third output of the timing section is a pulse indicating theoccurrence of the front porch of the horizontal sync pulse. This frontporch pulse is provided by using any of several front porch pulsedetector circuits (not shown) and is used by the DC restore circuit 24to set the blanking level to be compatible with the RS 170A standard.

In higher data rate transmission systems, a video analyzer 40 may alsobe included. The video analyzer 40 includes a digital signal processorthat analyzes the active portion of the video signal for informationrepresenting a group of pixels in a line representing a sharptransition. The video analyzer searches for signal informationrepresenting a sharp transition that would generate strong highfrequency clusters of the luminance or chrominance signals. Then, aninhibit signal is sent to both the elastic buffer 52 and the encoder 54.The inhibit signal is time shifted so that no secondary data is suppliedto the adder 70 when the primary video information representing thesharp transition is being outputted by the video portion 20. The use ofthe video analyzer 40 further reduces the possibility of interferencebetween the secondary data and the primary video. The video analyzer mayalso insert start and stop codes into the data stream so that thereceiver will recognize when data transmission has been inhibited toavoid interference.

The video analyzer 40 is only believed to be necessary in high data ratesystems such as T1 and above. For lower data rate systems, the videoanalyzer 40 and the inhibit signal may be eliminated. In those systemsthat have the video analyzer, the delay line 26 in the primary videosection 20 must delay the primary video signal sufficiently for the timeperiod for processing of a group of pixels by the analyzer 40. If thedata transmission rate is relatively low such as two hundred eightykilobits per second, however, the video analyzer 40 and the delay line26 may be eliminated.

The result at the output of the summer 70 is that the primary videosignal and the data are frequency interleaved. In addition, the combinedsignal from the summer 70 still has the same type of blanking intervalsfound in the standard NTSC signal. Therefore, the video signal may bereceived by a standard NTSC receiver without detecting the secondarytransmitted data.

To further ensure against interference, the output signal levels of thenoise interference section 60 and the secondary data section 50 shouldbe scaled. The scaling should set the injection level of those twosections to the adder 70 to avoid interference. The output level of thenoise interference section 60, should be adjusted to minimize noise onthe received data signal at a receiver. The output level of the datasection 50 should be adjusted so that there is no noticeableinterference on a video monitor coupled to the output of the adder 70.

In certain applications, it may be desirable to transmit an additionallow frequency signal such as an audio signal. For example, an audiosignal may be sampled using compression techniques such as in U.S. Pat.No. 5,021,786 and be transmitted during the horizontal sync intervals.If the secondary data is for example compressed video, the audio signalfor both a right and a left audio channel for the compressed video maybe sampled twice during each active interval and added during thehorizontal sync pulses. A multiplexer controlled by the timing signalmay be used for adding the compressed digital data during the horizontalsync pulses.

FIG. 2 shows a signal processor 100 for a video receiver that separatesthe transmitted data from the signal transmitted by a video transmitterincorporating the processor 10 of FIG. 1. Again, although thisembodiment is shown for receiving a primary NTSC signal having secondarydigital data frequency interleaved with the video, other embodiments mayuse for other video signals and primary data.

In FIG. 2, the received baseband signal, containing both video anddigital information is processed by two sections, a video section 120, atiming circuit 130 and a video analyzer section 140. The video section120 processes the received baseband signal through an automatic gaincontrol amplifier 122 and a DC restore circuit 124. The output of the DCrestore circuit is supplied to a band pass/comb filter 123. The outputof the band pass/comb filter 123 in the receiver 110 is to pass theinterleaved frequencies containing the transmitted data signals but toblock the primary video signal. The output of the band pass/comb filter123 is supplied to a phase compensator 125 that adjusts for phasedistortion due to the band pass/comb filter 123. The phase compensator125 may be a second filter restoring phase linearity with frequency toadjust for the phase distortion introduced by the band pass/comb filter123.

The phase compensated output signal is a reproduction of the rasterizedand modulated data signal supplied to the adder 70 by the data portion50. The rasterized modulated data signal is supplied to a data detector126, which also receives a system clock signal. The data detector 126comprises a peak detector that detects the peak signal in each period ofthe system clock and an envelope detector. For a data receivercompatible with a data transmitter of FIG. 1, the data detector outputis preferably a digital signal that represents a one when a data carrierhalf cycle is present and a zero when a data carrier half cycle is notpresent. For lower data rates, the processor 100 may look for thepresence of a data carrier over several cycles.

Although the above mentioned data detector 126 is designed for thetransmitter 10, it should be understood that the data detector may be ofany other format that has been chosen to be compatible with the datatransmission or modulation format of the transmitter 10. For example,the data detector may be a phase detector if the data is phasemodulated, or a quadrature amplitude detector if the transmitter usesquadrature amplitude modulation for the data. Further, if the data rateis sufficiently low where a bit of data is transmitted over severalcycles, for example 64 kilobits per second, the data detector may be theaforementioned envelope detector.

At high data rates, a circuit for detecting synchronously modulated datamay be needed. A clock recovery circuit may be used for recovering theclock from the data. That recovered clock may be used for sampling themodulated data. That sampled, modulated data may be provided to ananalog to digital converter to produce a digital signal. Alternatively,a low pass filter, a rotator and a slicer may be used with the datadetector.

The output of the data detector 126 is supplied to a data separator anddecoder 128 that provides the digital data as an output. The dataseparator and decoder 128 receives from the timing circuit 130 a timeadjusted composite blanking signal, and a regeneration of the datacarrier outputted by the timing circuit 30. The data separator anddecoder 128 also receives a video inhibit signal from a video analyzer140. The data decoder 128 uses the data level bits for each clockperiod, the data carrier, the blanking composite signal and the inhibitsignal to provide data at the same clock rate at the output as the dataprovided to the elastic buffer 52 of the transmitter. The data decoderand separator 128 will also remove the encoding provided by the encoder54 in the transmitter 10.

The output of the separator 128 is provided to an first in first outelastic buffer 129. The rate at which data is inputted to the buffer 129is controlled by the system clock from the timing block 130. The datamay be outputted from the buffer by a second clock (not shown) at anydesired data rate that prevents the buffer from overflowing.

The video analyzer 140 and the timing block 130 operate in the manner ofthe timing section 30 and the video analyzer 40 in the transmitter 10.The analyzer 140 and the timing block 130 prevent the data decoder andseparator 128 from reading blanking intervals in the rasterized data orinhibit periods transmitted in the data. So that the data signal will beproperly recovered a delay line (not shown) should be included beforethe data detector, where the delay line compensates for the processingperiod of the video analyzer 140.

It should be noted however, that if the video analyzer 40 of FIG. 1inserts start/stop codes in the data stream when data transmission isinhibited due to interference considerations, the receiver does not needa video analyzer 140. Instead, the data detector and separator 128 maydetect these start/stop codes as part of the decoding function.

Although the foregoing embodiment is designed for a primary video signalthat is in the NTSC format and transmitting secondary digital data forfrequency interleaving, other embodiments of the instant invention maybe used. The primary video signal for transmission may be for example asignal in the PAL or the SECAM format, any rasterized HDTV signal, orany other signal that has been rasterized. Further, the data may beanalog or digital data and the transmission and reception formats may besynchronous or non-synchronous depending upon the secondary data rate. Aparticular useful application for the disclosed invention is to transmita compressed video signal, ACTV signal or HDTV signal as the secondarydata signal.

By using the disclosed signal processors, the received video signal maybe demodulated and recovered by an ordinary video receiver without thetransmitted data causing noticeable interference on the televisionpicture generated by the receiver. The transmitted, secondary data mayalso be readily separated. It should be understood that the secondarydata provided to the signal processor may differ from the primary videosignal in a number of different aspects. Before being rasterized, thesecondary data signal has a low cross-correlation with the video signalas the two signals may be completely unrelated. Therefore, a widevariety of data may be transmitted and is particularly useful in systemswhere one way communications is preferred.

We claim:
 1. A method for transmitting data in the same communicationschannel as a video signal being transmitted in a given frequency band,the video signal having a video bandwidth with an upper frequency limitand active and blanking intervals with a sync frequency, and the videosignal and the data being uncorrelated with respect to each other, themethod comprising:detecting the active video intervals; and transmittingthe data at frequencies within the band and primarily near the upperfrequency limit of the band substantially centered around quarternon-integral multiples of the sync frequency during at least some of theactive video intervals.
 2. The method of claim 1, wherein the method fordetecting the active video intervals comprises detecting the blankingintervals of the video signal.
 3. The method of claim 2, wherein theintervals are defined by sync pulses, and wherein the video spectrumenvelope has gaps and transmitting the data comprises:generating a datacarrier at a frequency that is a quarter non-integral multiple of thesync frequency for modulating the data based upon at least some of theintervals between sync pulses; and modulating the data carrier with adata signal corresponding to the secondary data whereby the modulateddata carrier falls within the gaps of the video signal when modulated bythe data carrier, whereby frequency interleaving is obtained.
 4. Themethod of claim 2, wherein the step of transmitting the data furtherincludes blanking the data signal other than during the active videoperiod whereby the data signal is rasterized.
 5. A system for combininga data signal with a color frequency interleaved video signal having acolor carrier, audio information in a frequency band above frequencybands of luminance and chrominance information, horizontal sync pulsesat a predetermined rate and gaps in the video frequency bands with thespectral energy of the luminance and chrominance information separatedby about half the rate of the horizontal sync pulses, the systemcomprising:a timing circuit responsive to the sync pulses, the timingcircuit producing a data carrier at a frequency that is a non-integralmultiple of the rate and a timing signal indicating the time periods ofthe blanking interval; a combiner having at least two inputs; a videoportion providing the video signal to one input of the combiner; a dataportion providing a second input to the combiner; and the data portionincluding:a data buffer receiving the data and providing rasterized dataat an output based upon the blanking signal and the secondary data; amodulator for providing a modulated data signal responsive to the datacarrier and the output of the data buffer, the modulated data signalbeing coupled to the second input of the combiner such that the spectraof the modulated data signal lies substantially within the gaps of thevideo spectra and is primarily above the color carrier.
 6. The system ofclaim 5, the data portion further including a scrambler coupling therastorized data to the modulator, wherein the rastorized data receivedby the modulator is scrambled.
 7. The system of claim 5, wherein thedata signal includes a clock that controls the rate at which data isstored in the buffer.
 8. The signal processor of claim 5, wherein thesignal processor section further includes an encoder for limiting thebandwidth of the rasterized data.
 9. The signal processor of claim 5,wherein the video signal is an NTSC signal.
 10. The signal processor ofclaim 5, wherein the secondary data signal is a compressed video signal.11. The signal processor of claim 5, wherein the buffer is an elasticbuffer.
 12. The signal processor of claim 5, wherein the signalprocessor further includes a filter receiving the video signal andproducing as an output a signal that attenuates a reduced portion of thespectra of the video signal containing the video information.
 13. Thesignal processor of claim 5, wherein the signal processor furtherincludes means for detecting at least one of luminance and chrominancetransitions in the video signal above a predetermined limit and forinhibiting data transmission such that no modulated data is provided tothe combiner while the portion of the primary video signal containingthose transitions reaches the combiner.
 14. The signal processor ofclaim 5, wherein the signal processor further includes means fordetecting at least one of luminance and chrominance transitions in thevideo signal above a predetermined limit and for inserting a unique codein the modulated data to inform a receiver that transmission ofsecondary data will be halted temporarily.
 15. A signal processor forseparating a data signal from a rasterized video signal havinghorizontal and vertical blanking intervals at predetermined intervalsand frequencies and having chrominance and luminance informationfrequency interleaved through use of a color carrier having a frequencyin a bandwidth and clustered at a frequencies separated from each otherby about half the horizontal frequency and the data information beingcontained substantially in at least one unused portion of the samebandwidth, the processor comprising:a timing circuit generating a timingsignal at a predetermined frequency based upon the rate of thehorizontal intervals; a band pass filter having a lower cutoff frequencyof about the frequency of the color carrier and passing as an output thefrequencies for the data signal; and a data separator responsive to thetiming signal and the output of the filter for outputting the datasignal at a data rate above about 100 kilobits per second.
 16. Thesignal processor of claim 15, wherein transmission of the data signalhas been inhibited during intervals when the video signal representsrelatively sharp transitions between pixels and the processor comprisesa video processor for detecting information in the signal representingsharp transitions, and the separator further includes a datasynchronizer responsive to the video processor.
 17. The processor ofclaim 16, wherein the timing circuit outputs a pulse representing theblanking intervals and the separator uses the pulse to recognize theblanking intervals in the transmitted data signal.
 18. The processor ofclaim 15, further including a phase compensator for compensating thedata signal for any phase distortion of the filter, and the dataseparator further includes a synchronous data detector for detectingdata in the phase compensated data signal.
 19. A system for adding asecondary data signal to a primary color video signal of a formataccording to a predetermined standard having blanking intervals definedby sync pulses and a frequency band, the frequency band of the primaryvideo signal including both chrominance and luminance energy frequencyinterleaved with each other by modulation with a chrominance subcarrier,the chrominance energy lying within the upper portion of the video band,the data signal being uncorrelated to the video signal, the systemcomprising:means for detecting at least some of the sync pulses in thevideo signal; means for modulating a data carrier having a frequencyabove the chrominance carrier but substantially within the band of theprimary video signal with the data to provide a modulated data signalhaving a frequency band near the modulated data carrier and at leastpartially overlapping the video band of the video signal between thedata and chrominance carriers; and means for combining the modulateddata signal with the video signal such that the data signal istransparent to a receiver designed to receive the video signal.
 20. Thesystem of claim 19, wherein the data signal synchronously modulates adata carrier.
 21. A process for removing data information combined withcolor video information in a combined, rasterized signal generated by achrominance subcarrier positioned in the upper portion of the videobandwidth and having a blanking interval, and a bandwidth of greaterthan 3.5 megahertz, the processor comprising:means for receiving thecombined signal; means for generating a data subcarrier based upon thefrequency of at least the blanking interval at a frequency above thefrequency of the chrominance subcarrier but within the bandwidth; meansresponsive to the detecting means for demodulating the data with thedata subcarrier; and means for derasterizing the data.
 22. The processorof claim 21 further including a means for attenuating the spectralenergy of the combined signal below the chrominance subcarrier beforedemodulating.
 23. A method for transmitting a data signal with arasterized color video signal of a standard format having a luminancesubcarrier, a chrominance subcarrier, the chrominance subcarrier beingat an odd half multiple of a rasterization frequency in the upper halfof the spectra of the video signal, and a bandwidth, the luminanceinformation and the chrominance information in the video signal beingfrequency interleaved, the method comprising:rasterizing the datasignal; generating a data subcarrier at a frequency above thechrominance subcarrier to generate a modulated data signal having aspectra; modulating the rasterized data signal with the data subcarrier,whereby the spectra of the modulated rasterized data signal lies atleast in part between the chrominance and data subcarriers; andcombining the modulated rasterized data signal with the video signal.24. The method of claim 23, the method further comprising attenuatingthe spectral energy of the video signal above the chrominance subcarrierfrequency before combining the signals.
 25. A processor for transmittinga data signal component with a rasterized color video signal componenthaving active video intervals separated by video blanking intervals, thebandwidth of the video signal being greater than 3.0 megahertz and thecolor information being frequency interleaved in the upper portion ofthe bandwidth of the video signal by a color carrier located within thefrequency band, the processor comprising:means for generating a firstrasterized data signal component having a data rate of at least about100 kilobits per second so that the data signal has data blankingintervals separating active data intervals; and means for combining therasterized data signal component with the video signal component withinthe portion of the bandwidth between the color carrier of the videosignal and the upper end of the bandwidth such that at least some of thevideo blanking intervals in the data signal substantially coincide withthe active video blanking intervals and substantially withoutinterference between the components of the combined signal.
 26. Theprocessor of claim 25, the processor further comprising:a means forattenuating the spectral energy of the video signal at least somefrequencies above 3.0 Megahertz before combining the video and the datasignals.
 27. The processor of claim 25, the processor comprising:meansfor modulating the rasterized data signal with a data subcarrier above3.0 megahertz and providing the modulated rasterized data signal to becombined with the video signal.
 28. The processor of claim 27, theprocessor comprising:means for generating the data subcarrier at aquarter non-integral multiple of the video signal for modulating therasterized data signal.
 29. A processor for extracting data informationhaving data blanking intervals coinciding with at least part of ablanking interval of a video signal, the data information having beenmodulated with a subcarrier at a quarter non-integral multiple of theblanking interval frequency, the video signal including a luminanceinformation a chrominance information that has been modulated by achrominance subcarrier above 3.0 megahertz, wherein the video signal hasscanning frequency, the processor comprising:means for generating ademodulation subcarrier at about quarter non-integral submultiple of thescanning frequency above the chrominance subcarrier; means forattenuating a least a portion of the portion of the video signal belowthe chrominance subcarrier; means for demodulating the data informationfrom the attenuated video signal with the demodulating subcarrier; andmeans for eliminating the blanking intervals in the data signal.
 30. Aprocess for extracting data information intermixed with videoinformation in a rasterized video signal having blanking intervalsaccording to one of a predetermined format, the video informationincluding luminance information modulated with a luminance subcarrier,chrominance information modulated with a chrominance subcarrier, thespectral energy of the data information being contained primarily in thefrequencies above the chrominance subcarrier, the processcomprising:generating a subcarrier at a frequency above the chrominancesubcarrier from the video signal; extracting the data information bydemodulating the video signal with the generated subcarrier; andremoving the blanking intervals from the extracted data information. 31.A method for transmitting a data signal having a data rate of greaterthan about 100 kilobits per second with a frequency interleaved,rasterized color video signal having blanking intervals, a bandwidth andunused portion of spectra within that bandwidth, and the colorinformation having been modulated by a color carrier in the upper halfof the video bandwidth, the method comprising:rasterizing the datasignal to have blanking intervals and active data intervals at afrequency greater than 100 kilobits per second; generating a datacarrier based upon the rasterized video signal having blanking intervalsat the upper edge of the bandwidth; modulating the data subcarrier withthe rasterized data signal such that the modulated, rasterized datasignal lies substantially within at least one of the unused portions ofthe spectra; and combining the modulated, rasterized data signal withthe video signal.
 32. The method of claim 31, chrominance information inthe video signal having been modulated by a subcarrier, the methodfurther comprising generating the subcarrier at a frequencysubstantially a quarter non-integral multiple of some of the blankingintervals and the frequency being above the frequency of the chrominancesubcarrier.
 33. A method for transmitting a data signal within thebandwidth of a part of a color video signal at baseband, the videosignal being one of a group comprised of NTSC, PAL and SECAM format witha color signal interleaved with a luminance signal by modulating thecolor information with a carrier at an odd multiple of a half horizontalline frequency, the method comprising:filtering at least part of thevideo signal above the video signal containing the color information;rasterizing the data signal; modulating the data signal with a carrierabove the frequency of the color signal and within the basebandbandwidth of the video signal; and injecting the modulating data signalinto the video signal.
 34. The method of claim 33, furthercomprising:generating the carrier at a quarter, odd multiple of thehorizontal line frequency.
 35. The method of claim 33,comprising:generating the carrier at about the upper end of the videobandwidth.
 36. An apparatus for injecting a data signal having a datarate into a frequency interleaved, rasterized, color video signal havingblanking intervals at a frequency, a bandwidth with an upper limit, acolor carrier, the method comprising:a rasterizer responsive to the datasignal to provide a rasterized data signal have blanking intervalsseparating active data intervals; a data carrier generator generating adata carrier at a frequency near the upper limit of the video bandwidth;a modulator responsive to the data carrier and the rasterized datasignal to produce a modulated, rasterized data signal; and a combinerresponsive to inject the modulated, rasterized data signal into thevideo signal at an injection level and such that the blanking intervalsin the two signals substantially coincide.
 37. The apparatus of claim36, wherein the data carrier is at a frequency that is at about a onequarter non-integral of the blanking interval frequency.
 38. Theapparatus of claim 36, wherein the injection level is such that thevideo signal is not perceptible to a viewer at a television receiverreceiving the combined signals.
 39. The apparatus of claim 36, whereinthe portion of the bandwidth of the video signal where the data signalis injected is filtered.